The technology related to the present invention will be explained, taking a numerical control system as an example. In various types of machine tools such as a machining center and a lathe, actual machining of a work (material to be lathed) requires driving of a table for fixing the work, a chuck, and a tool (machine tool). A spindle motor and a servo motor that rotate or position-control tools and works in order to perform machining, in accordance with programmed instructions, play the role of driving; apparatuses for actually rotating and controlling the spindle and servo motors are drive control apparatuses (AMP1, AMP2, AMP3, AMP4, and AMP5 in FIG. 11). In addition, a control system referred to as a numerical control system (NC apparatus, hereinafter) outputs instructions to the drive control apparatuses. FIG. 11 is a block diagram illustrating a conventional NC apparatus system. Reference numeral 2 denotes input/output connectors for transmitting and receiving instructions from the NC apparatus, for controlling a position, a speed, and the like, and data from the drive control apparatuses; Reference numeral 3 denotes communication cables for transmitting and receiving control information and the like, between the NC apparatus and the drive control apparatus or between the drive control apparatuses. An instruction from the NC apparatus is inputted through the input/output connector 2 and communicated to each of the drive control apparatuses by way of the communication cable 3 and an input/output connector 5. Each drive control apparatus that has received the instruction controls driving of a motor based on the information by a motor controlling unit 10. In this situation, feedback data and the like from the motor leaves the motor controlling unit 10, passes again through the communication cable 3 and the input/output connector 5, and then is received by the NC apparatus through the input/output connector 2.
From the fail-safe point of view in which, when an emergency-stop signal is generated or when an interruption of a signal occurs at any position within communication circuits, it is determined that an emergency stop is instructed, a dedicated emergency-stop-signal transmitting and receiving cable independent from the communication cable 3 for the control data has been provided as an emergency-stop signal line. Reference numeral 1 denotes an emergency-stop switch utilized upon an emergency stop; the in-bound emergency-stop signal is received by the NC apparatus through a receiver 8 mounted in the NC apparatus, and is outputted by a driver 9 to the drive control apparatus by way of the emergency-stop-signal transmitting and receiving cable 4. Similarly, each drive control apparatus receives through a receiver 6 the emergency-stop signal and outputs through a driver 7 emergency-stop data to the following drive control apparatus. With regard to an emergency-stop signal, its reliability is most important and so it is required to prevent a malfunction. Therefore, in order to suppress effects of noise and the like, that cause the malfunction, in the emergency-stop-signal transmitting and receiving cables 4 between the NC apparatus and the drive control apparatus and between the drive control apparatuses, signals are utilized on a voltage level far higher than that of a control signal utilized within the drive control apparatus. In addition, in some cases, signals are transmitted and received as differential signals also in order to prevent the malfunction. Accordingly, due to the difference in the voltage level and the data format, the motor controlling unit is not able to deal with the emergency-stop signal; therefore, data that is inputted and outputted through the receiver 6, the driver 7, the receiver 8, and the driver 9 is converted with regard to an electric level, and the differential signals are converted.
The drive control apparatus that has received through these receivers the emergency-stop signal from the NC apparatus processes in the motor controlling unit 10 the emergency-stop signal, immediately halts the motor, and cuts off driving power for the motor. In addition, in the case where, as belt conveyer lines arranged in parallel to one another, each of systems controlled by the NC apparatus does not physically interfere with one another, and, even though one system is to be halted, other systems need to be operated, it is impossible to output the emergency-stop line from a single driver. Therefore, in the case where a plurality of systems are divided as illustrated in FIG. 11, in a conventional system in which an emergency stop line should be provided separately from a communication system line, a dedicated emergency-stop-signal transmitting and receiving cable 13 including an emergency stop button 12, for a system 2, should be provided, in addition to the emergency stop button 1 and the emergency-stop-signal transmitting and receiving cable 3, for a system 1.
With regard to the emergency stop line, reliability is most important from the fail-safe point of view; therefore, it has been indispensable to provide a dedicated line independent from a data communication line (the communication cable 3) for controlling systems. Accordingly, there has been a problem in that, in carrying out connection between the NC apparatus and the drive control apparatus and between drive control apparatuses for respective axles, wiring for the data communication cable 3 and the emergency-stop-signal transmitting and receiving cables 4 and 13 has been complex.
Moreover, in the case where a plurality of systems are controlled by the same NC apparatus, the number of connectors provided for connecting emergency stop lines needs to be increased with increase of the number of systems; therefore, problems, such as raised complexity of a system configuration through hardware and increase in costs, have occurred.
Furthermore, in order that, even though an emergency-stop signal is affected by noise or the like, in a path between the NC apparatus and the drive control apparatus, or between drive control apparatuses for respective axles, no lost portion and no extinction of the emergency-stop signal occurs, the voltage level of the signal is raised higher than the voltage level utilized in the motor controlling unit, and, in some cases, differential signals are utilized; in consequence, a problem is posed that a signal level converter or the like is required in each drive control apparatus.
In order to reduce a dedicated line for an emergency stop, there is an approach in which, by embedding an emergency-stop signal in a frame of serial data for communication, emergency stop is carried out simply through a communication line; as examples of a conventional art, “Terminal-Apparatus Monitoring System in Ring-Shape Communication System” (Japanese Laid-Open Patent Publication No. 1992-167835) and “Loop-Shaped Light Transmission System” (Japanese Laid-Open Patent Publication No. 1989-141442) disclose an approach in which a warning is contained in a frame. In addition, as another conventional art, “Controlling Method for Distributed Remote-I/O Control System” (Japanese Laid-Open Patent Publication No. 1996-328636) discloses an approach in which, by adding CRC (Cyclic Redundancy Check) codes to serial data in a frame, the serial data is automatically checked.
However, in the foregoing “Terminal-Apparatus Monitoring System in Ring-Shape Communication System”, only one serial-data frame for transmitting data is provided in each of ring-shaped communication loops, and the frame contains as warning bits warning information for all terminal apparatuses; therefore, measures against the case where a bidirectional communication is simultaneously defective are imperfect, and the system has a disadvantage in responding quickly because a principal apparatus determines treatment for the warning and then outputs instructions to terminal apparatuses. Moreover, similarly, the foregoing “Loop-Shaped Light Transmission System” is a system in which, for warning information outputted by a terminal apparatus, the principal apparatus by all means determines and outputs treatment for the warning; therefore, the system has the same disadvantage as the “Terminal-Apparatus Monitoring System in Ring-Shape Communication System” has.
Furthermore, in the foregoing “Controlling Method for Distributed Remote-I/O Control System”, an error and the number of frames are monitored by means of the CRC codes; however, all the checks are carried out by the principal apparatus, whereby the system has disadvantage in reliability in the case where the principal apparatus is out of order.